1、A Pyroelectric Infrared Sensor-based Indoor Location-Aware System for the Smart HomeSuk Lee, Member, IEEE, Kyoung Nam Ha, Kyung Chang Lee, Member, IEEEAbstract：Smart home is expected to offer various intelligent services by recognizing residents along with their life style and feelings. One of the k
2、ey issues for realizing the smart home is how to detect the locations of residents. Currently, the research effort is focused on two approaches: terminal-based and non-terminal-based methods. The terminal -based method employs a type of device that should be carried by the resident while the non-ter
3、minal-based method requires no such device. This paper presents a novel non-terminal-based approach using an array of pyroelectric infrared sensors (PIR sensors) that can detect residents. The feasibility of the system is evaluated experimentally on a test bed.Key words： smart home, location-based s
4、ervice, pyroelectric infrared sensor (PIR sensor), location-recognition algorithmI. INTRODUCTIONThere is a growing interest in smart home as a way to offer a convenient, comfortable, and safe residential environment 1, 2. In general, the smart home aims to offer appropriate intelligent services to a
5、ctively assist in the residents life such as housework, amusement, rest, and sleep. Hence, in order to enhance the residents convenience and safety, devices such as home appliances, multimedia appliances, and internet appliances should be connected via ahome network system, as shown in Fig. 1, and t
6、hey should be controlled or monitored remotely using a television (TV) or personal digital assistant (PDA) 3, 4. Fig. 1. Architecture of the home network system for smart homeEspecially, attention has been focused on location-based services as a way to offer high-quality intelligent services, while
7、considering human factors such as pattern of living, health, and feelings of a resident 5-7. That is, if the smart home can recognize the residents pattern of living or health, then home appliances should be able to anticipate the residents needs and offer appropriate intelligent service more active
8、ly. For example, in a passive service environment, the resident controls the operation of the HVAC (heating, ventilating, and air conditioning) system, while the smart home would control the temperature and humidity of a room according to the residents condition. Various indoor location-aware system
9、s have been developed to recognize the residents location in the smart home or smart office. In general, indoor location-aware systems have been classified into three types according to the measurement technology: triangulation, scene analysis, and proximity methods 8. The triangulation method uses
10、multiple distances from multiple known points. Examples include Active Badges 9, Active Bats 10, and Easy Living 11, which use infrared sensors, ultrasonic sensors, and vision sensors, respectively. The scene analysis method examines a view from a particular vantage point. Representative examples of
11、 the scene analysis method are MotionStar 12, which uses a DC magnetic tracker, and RADAR 13, which uses IEEE 802.11 wireless local area network (LAN). Finally, the proximity method measures nearness to a known set of points. An example of the proximity method is Smart Floor 14, which uses pressure
12、sensors.Alternatively, indoor location-aware systems can be classified according to the need for a terminal that should be carried by the resident. Terminal-based methods, such as Active Bats, do not recognize the residents location directly, but perceive the location of a device carried by the resi
13、dent, such as an infrared transceiver or radio frequency identification (RFID) tag. Therefore, it is impossible to recognize the residents location if he or she is not carrying the device. In contrast, non-terminal methods such as Easy Living and Smart Floor can find the residents location without s
14、uch devices. However, Easy Living can be regarded to invade the residents privacy while the Smart Floor has difficulty with extendibility and maintenance.This paper presents a non-terminal based location-aware system that uses an array of pyroelectric infrared (PIR) sensors 15, 16. The PIR sensors o
15、n the ceiling detect the presence of a resident and are laid out so that detection areas of adjacent sensors overlap. By combining the outputs of multiple PIR sensors, the system is able to locate a resident with a reasonable degree of accuracy. This system has inherent advantage of non-terminal bas
16、ed methods whileavoiding privacy and extendibility, maintenance issues. In order to demonstrate its efficacy, an experimental test bed has been constructed, and the proposed system has been evaluated experimentally under various experimental conditions. This paper is organized into four sections, in
17、cluding this introduction. Section II presents the architecture of the PIR sensor-based indoor location-aware system (PILAS), and the location-recognition algorithm. Section III describes a resident-detection method using PIR sensors, and evaluates the performance of the system under various conditi
18、ons using an experimental test bed. Finally, a summary and theconclusions are presented in Section IV.II. ARCHITECTURE OF THE PIR SENSOR-BASED INDOORLOCATION-AWARE SYSTEMA. Framework of the smart homeGiven the indoor environment of the smart home, an indoor location-aware system must satisfy the fol
19、lowing requirements. First, the location-aware system should be implemented at arelatively low cost because many sensors have to be installed in rooms of different sizes to detect the resident in the smart home. Second, sensor installation must be flexible because the shape of each room is different
20、 and there are obstacles such as home appliances and furniture, which prevent the normal operation of sensors. The third requirement is that the sensors for the location-aware system have to be robust to noise, and should not be affected by their surroundings. This is because the smart home can make
21、 use of various wireless communication methods such as wireless LAN or radio-frequency (RF) systems, which produce electromagnetic noise, or there may be significant changes in light or temperature that can affect sensor performance. Finally, it is desirable that the systems accuracy is adjustable a
22、ccording to room types.Among many systems that satisfy the requirement, the PIR sensor-based system has not attracted much attention even though the system has several advantages. The PIR sensors,which have been used to turn on a light when it detects human movement, are less expensive than many oth
23、er sensors. In addition, because PIR sensors detect the infrared wavelengthemitted from humans between 9.410.4 m, they are reasonably robust to their surroundings, in terms of temperature, humidity, and electromagnetic noise. Moreover, it ispossible to control the location accuracy of the system by
24、adjusting the sensing radius of a PIR sensor, and PIR sensors are easily installed on the ceiling, where they are not affected by the structure of a room or any obstacles. Figure 2 shows the framework for the PILAS in a smart home that offers location-based intelligent services to a resident. Within
25、 this framework, various devices are connected via a home network system, including PIR sensors, room terminals, a smart home server, and home appliances. Here, each room is regarded as a cell, and the appropriate number of PIR sensors is installed on the ceiling of each cell to provide sufficient l
26、ocation accuracy for the location-based services. Each PIR sensor attempts to detect the resident at a constant period, and transmits its sensing information to a room terminal via the home network system. Fig. 2. Framework of smart home for the PILAS.Consequently, the room terminal recognizes the r
27、esidents location by integrating the sensor information received from all of the sensors belonging to one cell, and transmits the residents location to the smart home server that controls the home appliances to offer location-based intelligent services to the resident.Within this framework, the smar
28、t home server has the following functions. 1) The virtual map generator makes a virtual map of the smart home (generating a virtual map), and writes the location information of the resident, which is received from a room terminal, on the virtual map (writing the residents location). Then, it makes a
29、 moving trajectory of the resident by connecting the successive locations of the resident (tracking the residents movement). 2) The home appliance controller transmits control commands to home appliances via the home network system to provide intelligent services to the resident. 3) The moving patte
30、rn predictor saves the current movement trajectory of the resident, the current action of home appliances, and parameters reflecting the current home environment such as the time, temperature, humidity, and illumination. After storing sufficient information, it may be possible to offer human-oriente
31、d intelligent services in which the home appliances spontaneously provide services to satisfy human needs. For example, if the smart home server “knows” that the resident normally wakes up at 7:00 A.M. and takes a shower, it may be possible to turn on the lamps and some music. In addition, the tempe
32、rature of the shower water can be set automatically for the resident.B. Location-recognition algorithmIn order to determine the location of a resident within a room, an array of PIR sensors are used as shown in Fig. 3. In the figure, the sensing area of each PIR sensor is shown as a circle, and the
33、sensing areas of two or more sensors overlap. Consequently, when a resident enters one of the sensing areas, the system decides whether he/she belongs to any sensing area by integrating the sensing information collected from all of the PIR sensors in the room. For example, when a resident enters the
34、 sensing area B, sensors a and b output ON signals, while sensor c outputs OFF signal. After collecting outputs, the algorithm can infer that the resident belongs to the sensing area B. According to the number of sensors and the arrangement of the sensors signaling ON, the residents location is dete
35、r-mined in the following manner. First, if only one sensor outputs ON signal, the resident is regarded to be at the center of the sensing area of the corresponding sensor. If the outputs of two adjacent sensors are ON, the residents location is assumed to be at the point midway between the two senso
36、rs. Finally, if three or more sensors signal ON, the resident is located at the centroid of the centers of the corresponding sensors. For example, it is assumed that the resident is located at point 1 in the figure when only sensor a signals ON, while the resident is located at point 2 when sensors
37、a and b both output ON signals. The location accuracy of this system can be defined the maximum distance between the estimated points and the resident. For example, when a resident enters sensing area A, the resident is assumed to be at point 1. On the assumption that a resident can be represented b
38、y a point and the radius of the sensing area of a PIR sensor is 1 m, we know that the location accuracy is 1 m because the maximum error occurs when the resident is on the boundary of sensing area A. Alternatively, when the resident is in sensing area B, the resident is assumed to be at point 2, and
39、 the maximum location error occurs when the resident is actually at point 3. In this case, the error is 3 / 2 m which is the distance between points 2 and 3. Therefore, the location accuracy of the total system shown in Fig. 3 can be regarded as 1 m, which is the maximum value of the location accura
40、cy of each area. Since the number of sensors and the size of their sensing areas determine the location accuracy of the PILAS, it is necessary to arrange the PIR sensors properly to guarantee the specified system accuracy.Fig. 3. The location-recognition algorithm for PIR sensors.In order to determi
41、ne the residents location precisely and increase the accuracy of the system, it is desirable to have more sensing areas with given number of sensors and to have sensing areas of similar size. Fig. 4 shows some examples of sensor arrangements and sensing areas. Fig. 4(a) and 4(b) show the arrangement
42、s with nine sensors that produce 40 and 21 sensing areas, respectively. The arrangement in Fig. 4(a) is better than Fig. 4(b) in terms if the number of sensing areas. However, the arrangement in Fig. 4(a) has some areas where a resident can not be detected and lower location accuracy than that in Fi
43、g. 4(b). Fig. 4(c) shows an arrangement with twelve sensors that five 28 sensing areas without any blind spots.Fig. 4. Location accuracy according to the sensor arrangement of PIRsensors. (a) 40 sensing areas. (b) 21 sensing areas. (c) 28 sensing areaswith twelve sensors.When PIR sensors are install
44、ed around the edge of a room, as shown in Fig. 4(c), it sometimes may give awkward results. One example is shown in Fig. 5. Fig. 5(a) shows the path of a resident. If we mark the estimated points by using the sensor location or the midpoint of adjacent sensors, it will be a zigzagging patterns as sh
45、own in Fig. 5(b). In order to alleviate this, we may regard the sensors on the edges to be located a little inwards, which give the result shown in Fig. 5(c).Fig. 5. The effect of compensating for the center point of the outer sensors.(a) Residents movement. (b) Before compensating for the outer sen
46、sors. (c)After compensating for the outer sensors.III. PERFORMANCE EVALUATION OF THE PILASA. Resident-detection method using PIR sensorsSince the PILAS recognizes the residents location by combining outputs from all the sensors belonging to one cell, determining whether a single sensor is ON or OFF
47、directly influences location accuracy. In general, because the ON/OFF values can be determined by comparing a predefined threshold and the digitized sensor output acquired by sampling the analog signal from a PIR sensor, it is necessary to choose an appropriate signal level for the threshold. For ex
48、ample, Smart Floor, which is another non-terminal method, can recognize a residents location exactly by comparing the appropriate threshold and a sensor value, because a pressure sensor outputs a constant voltage based on the residents weight when he remains at a specific point. However, because a P
49、IR sensor measures the variation in the infrared signal produced by a moving human body, its output is in analog form, as shown in Fig. 6. That is, as the variation in the infrared radiation from a resident increases when a resident enters a sensing area, the PIR sensor outputs an increasing voltage. Conversely, the voltage decreases as the resident leave the sensing area. If the resident does not move within the sensing area, the
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